The present invention relates in general to automobile burglar alarm devices, and more particularly to an automobile burglary alarm specially designed for protecting automobiles in public parking lots, having connections to the battery and the headlight and horn circuits of the automobile for monitoring battery voltage and thereby sensing when the domelight or the trunklight is turned on by burglar entry for energizing the automobile headlights and horn.
Heretofore, various automobile burglar alarm devices have been provided to respond to opening of automobile doors or breakage of glass or other illegal entry into an automobile when parked on public streets or in public parking lots to produce some kind of attention demanding indication of burglar entry into the automobile. Frequently these devices may be provided with switches or electrical circuit elements of various types associated with the doors, trunk, and/or windows or other portions of the automobile to cause a circuit to be activated when the switch or other access area monitoring device senses unauthorized entry into the automobile. Several such devices have employed sound detector transducers to sense certain sounds associated with breakin of the vehicle to activate an audible alarm or some other indicator of illegal entry into the automobile, and some of such devices have relied upon photoelectric sensors to respond to the light generated when the domelight turns on or when some special event associated with burglar entry occurs. It is desired to devise an automobile burglar alarm which will be relatively inexpensive to manufacture and highly reliable in operation, which avoids the necessity of using expensive photoelectric or sound transducer devices and circuitry and which can make use of the existing headlight and horn circuits of the automobile to produce alarm signals indicating unauthorized burglar entry into the automobile.
An object of the present invention, therefore, is the provision of a novel burglar alarm device for automobiles having undervoltage sensing circuitry for monitoring the battery voltage of the automobile battery to detect reduced battery voltage conditions, when placed in a burglar alarm mode, to sense when the domelight or trunklight of the automobile is turned on by burglar entry, and to activate the automobile headlight and horn circuits to indicate burglar entry.
Another object of the present invention is the provision of a novel burglar alarm device for automobiles of the type described in the immediately preceding paragraph, provided with delay circuitry to delay activation of the automobile headlight and horn circuits when battery voltage reduction occurs, for a short period enabling the burglar alarm device to be switched off by the owner, when the owner enters the automobile to provide for owner cutoff opportunity.
Other objects, advantages and capabilities of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawing illustrating a preferred embodiment of the invention.